1. Field of the Invention
The present invention relates to methods of manufacturing large-diameter piping and is specifically concerned with a method of producing crack arrester.
2. Description of Related Art
The laying of trunk pipelines, expecially in the Arctic, has given rise to the problem of protecting the piping against longitudinal failures.
With an increase in gas pressure and pipe diameter, the potential energy accumulated in the pipeline greatly increases and the task of limiting the extent of failure appears to be complicated. Studies have shown that ductile failures can be mitigated with a probability of a given order if the toughness of the steel used is increased 1.5-2 times compared with the existing values. However, the rapid structural changes taking place in the wall of a pipe during its failure interfere with the mechanism of plastic deformation and prevent full capitalization of the high toughness of steel achieved at a high price.
It must be also taken into account that the potentiality of steel-casting and plate-rolling plants in producing steel of requisite toughness and strength at an economically-acceptable cost is limited. It appears that under the existing conditions an optimum method of limiting the propagation of longitudinal ductile failures consists in building pipelines of a steel not liable to brittle failure and incorporating thereinto at strategical points crack arresters ensuring that every propagating crack will be stopped within their length.
Generally known are crack arresters in the form of a pipe length of the same diameter as the pipeline and enshrouded with strip or rope. The elastic energy released while the crack propagates is absorbed by the strip or rope with the result that the crack cannot widen, changes its trajectory from rectilinear to a helical one and is stopped eventually.
These crack arresters invite difficulties in laying pipelines and increase the cost of said projects.
Recently a crack arrester for trunk pipelines has been developed (cf. U.S. Pat. No. 4,383,556; Int. Cl..sup.3 F 161 13/02; 1983) which is made in the form of a multi-layer pipe section with a diameter and wall thickness equalling those of the pipeline and is provided with specially shaped slots in inner layers.
The slots at the edges of multi-layer crack arresters pose problems in placing circumferential welds at the site. Multilayer pipe sections display a reduced stiffness which increases difficulties in handling and welding the piping.
Also known is a method of producing multi-layer crack arresters consisting of winding a slotted strip around a pipe section of a diameter and wall thickness equalling those of the pipeline, welding the inner and outer lap joints to each other, and welding solid wall pipe lengths to each end face of the crack arrester at the shop which are intended to facilitate the fitting of the crack arrester to the pipeline at the site (cf. Trudy VII sovmestnogo sovetsko-zapadnogermanskogo simposiuma s knotsernom Mannesman AG po trubam bolshogo diametra; B. E. Paton, S. M. Biletsky, A. A. Rybakov, Yu. P. Barvinko "Truby i gasiteli razrusheniy s mnogosloinoy stenkoy dlya magistralnykh gazoprovodov", Minneftegasstroy Publishers, Moscow, pp. 8-11, 1982).
The solid-wall pipe lengths added to the crack arrester reduce the effect obtained from applying the known method of producing crack arrester.